XC90 error code woes & poor fuel economy

[blankenship]

I've got a 'new to me' '05 XC90 with 180k that has a pretty tremendous service history, but I've been getting engine codes repeatedly and am only averaging 15mpg on the 2.5T engine with conservative driving. Also, I notice some stronger-than-usual exhaust fumes if I'm outside the car at idle.

Codes are a consistent P2196 "O2 sensor signals biased/stuck rich bank 1 sensor 1" -
And I also sometimes get a P0026 Intake valve control solenoid circuit range/performance bank 1"
and P0027 Exhaust valve control solenoid circuit range/performance bank 1."

I've done some searching on the forum, and seems like there could be a wide variety of culprits...
Would appreciate if anyone has a hunch on likeliest culprit?!

[ggleavitt]

Might need to check your oil pressure, for this age vehicle there could well be a problem coming from your oil pan. Service history notwithstanding, it's a 22 year old motor and has a few seals in the that may have hardened up. See viewtopic.php?p=142626#p142626 for a thread with some visuals. Error codes are telling you that the VVT hub is not reaching the "target" angle in the required amount of time. As the hub is driven by a solenoid and oil pressure, a reduction in pressure will directly affect the swing time. Might not be your issue but since it's both solenoids, could be a faster path to check as a start.

My immediate thoughts as based on your symptoms.

[blankenship]

I replaced the O2 sensor, and that code hasn't reappeared, BUT:

Fuel economy has now DROPPED from 15mpg to 13mpg.
Car sounds almost like a small diesel at idle.

The intake/exhaust VVT solenoid errors persist - I'm unsure how to check oil pressure, but haven't had any oil pressure lights illuminate on dash.

Do you think these are related?

FYI, replaced all spark plugs (Bosch Platinum FR7DPP) just 1,000 miles ago and air filter looks good. Fuel pump replaced 7k ago, and fuel filter replaced 20k ago.

[Krons]

Was oil changed every 5000 miles or 7500? Guessing your VVT solenoids could be sludged and varnished up. Easy to pull them off and give a look underneath.

Not sure seal issues would impact fuel consumption, could though if VVT circuit is starved for oil. My kids 02 S60 2.4T was getting erratic oil pressure light and I did drop the oil pan to find the oil pickup tube orings hard/brittle and sucking air. New orings fixed it up. No fuel consumption problem though.

Fuel consumption should be spark/fuel/air related, with newer spark plugs (I assume you’ve changed the air filter) I would try some fuel system cleaner to see if cleaning up the injectors would help. I’m always surprised what a few tanks of Marvel Mystery Oil will do.

I’m two months into a new to my kid '05 XC90 2.5T also (190k), seems in town 15mpg is about normal, maybe 20 on highway. Much heavier than my 08 S60 2.5T that’s nearly 50% better mpg.